Simple flexible joint for high pressure and high temperature

ABSTRACT

A flexible joint for providing a hinged connection with an underwater transport line or “riser” for transporting an oil or gas fluid and that is subjected to a traction force. The joint comprises a substantially cylindrical housing containing: a second tubular portion fixed to one end of said housing; a first tubular portion fixed to said underwater transport line and secured to a laminated hinge abutment fixed to another end of said housing and against which the traction force of said transport line is exerted; and tubular isolation means interconnecting said first and second tubular portions in such a manner as to confine the fluid passing through the flexible joint.

TECHNICAL FIELD

[0001] The present invention relates to the offshore oil industry, andmore particularly it relates to a simple flexible joint for use withhigh pressure and high temperature and designed to be fitted toconnection systems for risers (underwater lines carrying fluid).

PRIOR ART

[0002]FIG. 3 shows an example of a simple flexible joint 10 of the priorart as used in the offshore oil industry and designed to have its bottomportion connected (in general via a weld 12) to an underwater tubularstructure 14 or “riser” connected to a well head (not shown) in a gas oroil field that is to be worked, with its top portion connected (ingeneral by means of a plurality of bolts 16) to the head 18 of apipe-line 20 for carrying the extracted gas or oil fluid.

[0003] That conventional assembly includes a laminated spherical hingeabutment 30 made up of rigid layers, e.g. of metal, alternating withelastomer layers, the various layers being bonded to one another. Theabutment is housed between a strength member 32 in the form of aspherical cap and forming an integral portion of a first tubular portion34 of said assembly that is designed to be fixed to the extraction line14, and a strength member 36 constituted by a ring which is fixedlyconnected, e.g. by a plurality of bolts 38, to a second tubular portion40 of said assembly and presenting in the example shown the generalexternal shape of a bell surmounted by a flange 42 for receiving theline head 18. The faces of the layers of the abutment and the faces ofthe cap and of the ring between which the abutments are disposed areconcentric spherical surfaces centered on a common point O situated onthe flexible hinge axis (which coincides with the axis of the transportline). Internally, this tubular portion has a spherical emerging endportion 44 which is designed to come into contact with and cooperatewith the spherical cap 32 so as to avoid putting the laminated abutment30 under tension while the riser 14 is being installed.

[0004] That conventional structure gives complete satisfaction undermost circumstances of offshore use, in particular when the pressuresinvolved do not exceed 400 bars and the temperatures do not exceed 100degrees Celsius (° C.). Nevertheless, as liquid or gas hydrocarbonreserves become rarer, more and more fields are being worked in deepwater. Unfortunately, at very great depths (greater than 1500 meters(m)), the pressure and the temperature of the extracted fluid are bothvery high (greater than or equal to 600 bars and 120° C., respectively)and conventional assemblies of the kind described above cannot withstandthem, in particular because the laminated hinge is not protected fromthe fluid.

OBJECT AND DEFINITION OF THE INVENTION

[0005] An object of the present invention is to mitigate theabove-described drawbacks by proposing a simple flexible joint which canbe guaranteed to operate under extreme conditions of pressure andtemperature. Another object of the invention is to provide an assemblythat is particularly reliable and that also presents a long lifetime.Yet another object of the invention is to protect the laminated hingeeffectively against chemical attack by the fluid.

[0006] These objects are achieved by a flexible joint for providing ahinged connection with an underwater transport line or “riser” fortransporting an oil or gas fluid and that is subjected to a tractionforce, the joint comprising a substantially cylindrical housingcontaining: a second tubular portion fixed to one end of said housing; afirst tubular portion fixed to said underwater transport line andsecured to a laminated hinge abutment fixed to another end of saidhousing and against which the traction force of said transport line isexerted; and tubular isolation means interconnecting said first andsecond tubular portions in such a manner as to confine the fluid passingthrough the flexible joint.

[0007] With this particular structure for a flexible joint, the fluidremains confined within the housing in a central channel that is definedin succession by the first tubular portion, the tubular isolation means,and the second tubular portion, thereby isolating the laminated hingeabutment from attack by the fluid.

[0008] The tubular isolation means comprise a spherical laminatedabutment which is preferably mounted between a first strength membersecured to said first tubular portion and a second strength membersecured to said second tubular portion, the strength membersadvantageously including sealing means of the O-ring type.

[0009] In an embodiment, the second spherical laminated abutment has acenter of rotation O in common with the center of rotation of said firstlaminated hinge abutment.

[0010] Advantageously, the housing has a plurality of slots for allowingseawater to flow through as a cooling fluid.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Other characteristics and advantages of the present inventionwill appear more clearly from the following description given by way ofnon-limiting indication and made with reference to the accompanyingdrawings, in which:

[0012]FIG. 1 is a longitudinal section view through a simple flexiblejoint of the invention for use with high pressure and high temperature;

[0013]FIG. 2 is an external perspective view of the simple flexiblejoint of FIG. 1; and

[0014]FIG. 3 is a longitudinal section view through a simple flexiblejoint of the prior art.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

[0015]FIGS. 1 and 2 are respectively a longitudinal section and an outerperspective view of a simple flexible joint of the invention for use inextracting hydrocarbons from very deep waters (depths in excess of 1500m) where pressure and temperature conditions are extreme, i.e. greaterthan or equal to 600 bars and 120° C. The joint itself is commonlylocated a little below the surface.

[0016] Like a conventional assembly, this assembly comprises a singlelaminated spherical hinge abutment 50 comprising rigid layers, e.g. ofmetal, alternating with layers of elastomer, the various layers beingbonded to one another. This abutment is also received between a firststrength member 52 in the form of a spherical cap on which there comesto rest a first tubular portion 54 of said assembly, which portion isshaped like a golf tee and is for welding (via a weld 56) to a fluidextraction line 14, and a second strength member 58 constituted by aring forming the bottom of this assembly and securely connected, e.g. bymeans of a first set of stud bolts 60 disposed circumferentially to asecond annular portion of the assembly. The connection between the capand the tee is advantageously a pressed connection (the abutment 50being precompressed during assembly) with mechanical cone-on-conecontact.

[0017] To make the assembly easier to assemble, the second tubularportion is advantageously made up of two parts (but it would naturallybe possible for it to comprise a one-part structure as in the prior art)comprising a cylindrical housing body 62 and a cover plate 64 coveringits top portion and surmounted by a flange 66 for receiving the linehead (not shown). The plate 64 is fixed to the cylindrical housing inthe same manner as the bottom 58 is fixed to the bottom portion of thehousing, by means of a second set of stud bolts 68 that are likewisedisposed circumferentially. The faces of the abutment layers and thefaces of the cap and of the ring between which the abutment is disposedare concentric spherical surfaces centered on a common point O situatedon the flexible hinge axis (which coincides with the axis of theextraction line).

[0018] As in a conventional assembly, the traction force exerted by theriser 14 is transmitted to the first tubular portion 54 of thecylindrical housing 62 by the laminated abutment 50 which alsoaccommodates angular variations of the riser 14 in all directions.

[0019] According to the invention, the laminated hinge abutment 50 isisolated from attack from the transported fluid by tubular isolationmeans 70 disposed between and in line with the first and second tubularportions to which they are connected to form a confinement channel 72for the fluid under pressure and at high temperature. For this purpose,the first tubular portion 54 is secured rigidly by first connectionmeans 74 (although a simple force-fit would also be possible) to ahemispherically-shaped first strength member 76 of a second laminatedabutment 78 whose ring-shaped second strength member 80 is securelyfixed by second connection means 82 to the plate 64 of the secondtubular portion. This second laminated abutment is likewise of astructure that is concentric about a center of rotation O in common withthat of the hinge abutment 50.

[0020] The confinement channel is frustoconical in shape, being ofsmaller section level with the first tubular portion and isolation ofthe fluid is reinforced by sealing means of the O-ring type 84, 86mounted firstly between the first strength member and the first tubularportion, and secondly between the second strength member and the coverplate, and preventing fluid from flowing towards the laminated hingeabutment 50. In addition, in order to ensure that heat is removedeffectively, the cylindrical housing includes a plurality of slots 88that are regularly distributed around its periphery and that allowseawater to flow inside the housing, thereby ensuring that it is at thesame pressure as the surrounding ocean. The particularly high internalpressure flowing in the transport line and passing through the jointtherefore does not act on this housing and thus does not act either onthe laminated hinge abutment 50.

[0021] With this particular structure, the laminated hinge abutment 50which takes up both tension from the line and angle variations due tothe riser 14 (i.e. which takes up mechanical forces), is completelyprotected from chemical attack, and also from the pressure and thetemperature of the fluid, by the second laminated abutment 78 whichperforms this separation function (confinement barrier) between thefluid and the hinge abutment 50. This second abutment which takes up thepressure of the fluid and which accompanies the variations of angle(because of its secure connection to the tee 54 fixed to the riser) can,in contrast, accommodate a certain amount of damage due to the fluidsince it has little influence on the overall mechanical strength of theassembly.

1/ A flexible joint for providing a hinged connection with an underwatertransport line or “riser” for transporting an oil or gas fluid and thatis subjected to a traction force, the joint comprising a substantiallycylindrical housing containing: a second tubular portion fixed to oneend of said housing; a first tubular portion fixed to said underwatertransport line and secured to a laminated hinge abutment fixed toanother end of said housing and against which the traction force of saidtransport line is exerted; and tubular isolation means interconnectingsaid first and second tubular portions in such a manner as to confinethe fluid passing through the flexible joint. 2/ A flexible jointaccording to claim 1, wherein said tubular isolation means include aspherical laminated abutment. 3/ A flexible joint according to claim 2,wherein said spherical laminated abutment is mounted between a firststrength member secured to said first tubular portion and a secondstrength member secured to said second tubular portion. 4/ A flexiblejoint according to claim 3, wherein said first and second strengthmembers include O-ring type sealing means. 5/ A flexible joint accordingto claim 1, wherein said second spherical laminated abutment has acenter of rotation O in common with that of said first laminated hingeabutment. 6/ A flexible joint according to claim 1, wherein said housingincludes a plurality of slots to allow seawater to flow through as acooling fluid.